As communication devices receive more widespread acceptance, and as various new uses for communication devices emerge, the need for more spectrally efficient communication becomes more evident. Spectrum efficiency has always been a challenge to communication system designers. One area of radio communication that has developed slowly because of its poor spectral efficiency is full duplex communication.
In this mode of operation, radio operators receive and transmit signals at the same time without having to take turns in transmitting to each other. However, full duplex operation is desired because it is the ultimate in communication and it is available in telephonic communication. Full duplex communication using Frequency Division Multiplexing (FDM) requires two channels, one for each transmitter. This requirement results in inefficient spectrum use because both channels are occupied even when information communication is unidirectional. Because of this disadvantage and the decrease in spectrum availability, full duplex communication in two way radios using FDM is substantially limited.
A Time Division Multiplexing (TDM) system using voice compression may provide full duplex communication with increased spectral efficiency. Similar to FDM systems, however, such a system requires dedicated time slots for transmission by each unit even when information communication is unidirectional which results in wasted channel bandwidth.
Another method of improving spectrum utilization is to have a control station manage the allocation of frequencies on a need to use basis. This requires an additional channel for the control signal and further complicates the operation of the communication device. It can therefore be seen that a communication device is highly desired that can operate full duplex with efficient spectrum utilization.